The ink jet print head of an ink jet printer generally consists of an orifice plate containing orifices or injection parts for discharging ink for recording on a substrate, ink passage ways connecting the orifices to an ink supply and an energy imparting device for ejecting ink from the print head through the orifices. The energy for discharging the ink during recording is generated in most cases by resistance elements or piezoelectric devices.
Methods for making the ink passage ways for ink jet print heads include, for example, forming fine grooves in a thin layer of glass, metal, or plastic by cutting or etching and then bonding another thin layer of material onto the layer having such grooves formed thereon to form liquid passage ways. Another method involves forming grooves in a photosensitive resin coated on a substrate containing the energy imparting device by photo lithographic techniques. Once the grooves are formed in the photosensitive resin another thin layered material is attached to the grooved resin to form, for example, nozzle plates.
Among these methods for preparing an ink jet print head, the use of a photosensitive resin to provide at least a portion of the ink passage layer is more advantageous than other methods since the liquid passage ways can be manufactured with higher precision and yield and liquid jet recording heads can be obtained with better quality and lower cost. The photosensitive resin is required to have (1) excellent adhesion as a cured film to a substrate; (2) excellent mechanical strength and durability, when cured; and (3) excellent sensitivity and resolution upon patterning with a radiation source.
Of the known photo curable resins, U.S. Pat. No. 4,623,676 describes a radiation curable composition for use as a protective coating for a photographic element containing a polymerizable acrylic compound, a polymerizable epoxy-functional silane, a free radical aromatic complex salt photoinitiator capable of initiating polymerization of said acrylic compound, and a cationic aromatic complex salt photoinitiator capable of initiating polymerization of said epoxy functional silane.
U.S. Pat. No. 4,688,053 describes a liquid jet recording head having a layer of a radiation curable resin composition containing a linear polymer having a glass transition temperature of at least 50/C and a weight average molecular weight of at least 3.0.times.10.sup.4, a monomer having an ethylenically unsaturated bond, an epoxy resin having one or more epoxy groups, and a polymerization initiator capable of generating a Lewis acid by irradiation with an active energy source.
U.S. Pat. No. 4,090,936 describes a photo hardenable composition containing an organic compound having an average epoxide functionality in the range of about 1 to 1.3; an organic polymer selected from polymers derived from acrylate or methacrylate monomers, copolymers of styrene and allyl alcohol, and polyvinyl butyral polymers; and an aromatic complex salt aromatic complex salt photoinitiator.
However, none of the known photosensitive resins provide all of the requisite characteristics for use in jet print head applications. For example, photosensitive resins used for pattern formation in printing plates, print wires, etc., have inferior adhesion to glass, metal, ceramic and plastic, and insufficient in mechanical strength and durability when cured although they may have good sensitivity and resolution. For these reasons when photosensitive resins are used in a print head, deformation or delamination from the substrate or degradation of the photosensitive resin layer are liable to occur during usage which reduces the reliability of the ink jet print head by impeding the flow of ink in the ink passage ways or making the ink droplet discharge noticeably unstable.
On the other hand, photo curable resins which adhere to glass, metal, ceramic and plastic, and provide satisfactory mechanical strength and durability after curing, are inferior in sensitivity and resolution. The inherent characteristics of photo curable resins makes them unsuitable for use in providing ink passage ways because they cannot be cured in the precise patterns required for use in ink jet print heads.
An object of the present invention is to provide an improved radiation curable resin for use in ink jet print heads.
Another object of the present invention is to provide an ink jet print head containing an ink passage layer made of a resin satisfying all of the requisite characteristics as mentioned above, which is inexpensive, precise, high in reliability and excellent in durability.
Yet another object of the present invention is to provide an ink jet print head having precisely manufactured ink passage ways.